On Jun 6, 6:36*pm, Wimpie wrote:
On 6 jun, 19:00, Richard Clark wrote:



On Sun, 6 Jun 2010 07:42:31 -0700 (PDT), Wimpie
wrote:

However a PA is not a 50 Ohms source

Hi Wimpie,

You say this like others, with the air of "knowing." *However, when I
ask in response of those who "know" what the PA is NOT, what IS it?

Give me the Z value of your transmitter. *Specify all initial
conditions.

We have had lengthy correspondence with Walt Maxwell's very rigorously
measured Kenwood TS830s that demonstrates a Z of 50 Ohms, or nearly
that as is practicable (say +/- 20%); and yet your voice was missing
from this discussion with evidence to the contrary.

73's
Richard Clark, KB7QHC

Hello Richard,

Walt did respond and did a solid statement regarding the amplifier
with matching section to obtain maximum output (so I know the
conditions) *This is the point where the tube/transistor is at the
edge of current/voltage saturation.

At that operating point the output impedance is 50 Ohms (for small
load variations). When you change the load significantly (or change
drive level), current or voltage saturation will dominate, hence the
output impedance is no longer 50 Ohms. * This is also the reason that
PA intermodulation may occur in close spaced transmitters where some
power from transmitter A enters the amplifier of transmitter B and
vice versa. This also proves that there is no linear 50 Ohms output
impedance.

Best regards,

Wim
PA3DJSwww.tetech.nl

Sorry Wim, I can't agree with some of your statements in your last
post. Concerning maximum output, I will agree that saturation will
occur when the minimum of the peak AC plate voltage equals the peak AC
grid voltage. This condition occurs when the tube is delivering its
total maximum possible power. However, when the grid drive level is
less than that which brings the plate-voltage minimum down to the grid-
voltage level, saturation does not occur.

In addition, when the pi-network has been adjusted to deliver all the
available power at some drive level less than the maximum possible
power, the source resistance at the output of the pi-network will be
exactly equal to its load resistance, not somewhat higher or lower.
This follows from the Maximum Power Transfer Theorem. This is not
speculation, but proof determined by data from many, many
measurements.

Walt, W2DU